Abstract
The concentration of mercury vapour in ambient air is routinely determined using specialised instruments.As an economical alternative, actively pumped Hopcalite sorbent tubes can be used to trap atmosphericmercury, which is subsequently analysed by cold vapour atomic absorption spectroscopy. Plant materialsare also readily available in most regions and can be analysed to obtain information on time averagedatmospheric mercury levels.Lichen and tree bark samples were collected in the cities of Pretoria and Witbank, dried and acid digestedwith subsequent cold vapour atomic absorption spectroscopy. Average mercury concentrations rangingfrom 74 to 193 μg.kg-1 were found in lichens from three Pretoria suburbs, whilst average Hg levels of 228μg.kg-1 were determined in lichens collected in Witbank. The average mercury concentration in tree barkwas consistently lower than in lichens, with concentrations between 28 and 72 μg.kg-1 determined insamples from three Pretoria suburbs and 75 μg.kg-1 determined in samples taken in Witbank. This study isthe first in South Africa to determine mercury levels in lichens and tree bark.Average total gaseous mercury concentrations in ambient air at the three Pretoria suburban sites, asdetermined by a semi-continuous spectroscopic method using Hopcalite sampling, ranged between 1.6and 2.5 ng.m-3, while an average of 1.7 ng.m-3 was measured in Witbank over the sampling interval.
Highlights
Anthropogenic activity is a major contributor to the atmospheric mercury burden
Lichen samples collected in Hatfield showed a significantly lower concentration (p
Within Pretoria, significantly higher atmospheric mercury concentrations were measured in Hatfield than in other areas (p
Summary
Anthropogenic activity is a major contributor to the atmospheric mercury burden. Sources include coal fired power plants, incinerators, chloralkali plants and battery production plants (Pacyna & Pacyna, 2002). South Africa has been rated as one of the largest emitters of mercury in the world with an estimated emission of 256 tons of mercury per annum (Pacyna et al, 2006), a lower estimate of 62 tons was determined for 2006 (Masekoameng et al, 2010). These emissions are largely the result of the country's use of coal as a primary energy source, and the relative density of coal fired power plants in the Highveld region would be suggestive of a potentially high atmospheric mercury burden in this area. It is important that local atmospheric Hg levels be determined to aid in the assessment of potential environmental impacts
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